Electrographic writing systems are well known. They comprise a writing head usually having a linear array of marking elements in the form of styluses or nibs for generating sequential raster lines of information by means of high voltage electrical discharges across a minute air gap to a conductive electrode. An insulating record medium, interposed between the styluses and the conductive electrode, retains thereon invisible electrostatically charged areas formed on its surface in response to the electrical discharges. Subsequently, the charged areas are rendered visible by the application of "ink", which may be in liquid or powder form, held to the medium by electrostatic attraction. the visible image may be fixed to the medium in any one of a variety of ways, to produce a permanent record. An example of such a writing system is disclosed in our parent patent application U.S. Ser. No. 678,146 filed Dec. 4, 1984, now U.S. Pat. No. 4,588,997 and entitled "Improved Electrographic Writing Head", fully incorporated herein by reference.
A fluid jet assisted ion projection printer, of the type utilized herein, is disclosed in commonly assigned U.S. Pat. No. 4,463,363 issued on July 31, 1984 in the names of Robert W. Gundlach and Richard L. Bergen, entitled "Fluid Jet Assisted Ion Projection Printing". In that printing system, an imaging charge is placed upon a moving receptor sheet, such as paper, by means of a linear array of closely spaced minute air "nozzles". The charge, comprising ions of a single polarity (preferably positive), is generated in an ionization chamber by a high voltage corona discharge and is then transported to and through the "nozzles" where it is electrically controlled, within each "nozzle" structure, by an electrical potential applied to an array of marking elements in the form of modulating electrodes. Selective control of the electrical potential applied to each of the modulating electrodes in the array will enable areas of charge and areas of absence of charge to be deposited on the receptor sheet for being subsequently made visible by suitable development apparatus.
A typical modulation structure for the ion projection type of printer is disclosed in U.S. Pat. No. 4,524,371 issued on June 18, 1985 in the names of Nicholas K. Sheridon and Michael A. Berkovitz and entitled "Modulation Structure For Fluid Jet Assisted Ion Projection Printing Apparatus". In that device, a planar marking head is mounted on the ion generating housing and each electrode thereon is addressed individually, for modulating each "nozzle" independently.
A high quality marking head of page width, i.e. about 8.5 inches wide, having a resolution of 200 to 400 spots per inch (spi), would result in an array of 1700 to 3400 marking elements. In order to simplify, and thereby reduce the cost of such a marking head, it would desirably include, on a single large-area substrate, a thin film marking element array, address lines, data lines, high and low potential bus lines, an inverter-type thin film switching circuit and a thin film latching circuit.
The primary object of the present invention is to provide an improved marking head, manufacturable by thin film fabrication techniques, including an electrical circuit in which marking elements are at all times electrically connected to either a source of high potential or a source of low potential.
It is a further object to provide a marking head wherein each of the marking elements will be controlled by a latching circuit and an inverter circuit for allowing each element to be connected to a source of marking potential through the inverter circuit, for substantially a line time, until the latching circuit is unlatched.